In my U.K. Pat. No. 1,532,995 I described a mounting device for such plates in the form of an elongate base strip having a plurality of heads projecting therefrom uniformly spaced along the strip, each head comprising a spaced pair of elements having mutually divergent portions on their surfaces remote from each other, whereby plates, whose flanges are spaced apart by a multiple of the unit centre-to-centre spacing of adjacent heads, can be resiliently push-fitted onto the strip which extends at right angles to direction of extension of the plates. The present invention provides a development of this device which is more versatile and more easily employed.